1. Field of the Invention
The present invention relates to an automatic guided vehicle that can automatically move between a freight transfer station and a freight loading station on the floor of a factory, warehouse or the like. More particularly, this invention relates to such an automatic guided vehicle which is capable of automatically performing loading and unloading operation of a carriage at predetermined positions on a running passage which is slightly larger in width than the vehicle width.
2. Description of the Prior Art
The most common freight-transport vehicle of the type having a freight transfer device for delivering freights is a forklift. The forklift of the type concerned is usually operated by an operator boarding thereon. In recent years, with the spread of unmanned or automatically operated transport vehicle, the freight transfer device has been automated. One example of such unmanned or automatic transport vehicle is called an automatic fork traverse (AFT). The AFT is operated to move, without an operator aboard, between a freight-stocker entrance and exit and a freight transfer station, for transporting a freight, and automatically perform loading and unloading operation by inserting and removing a fork from one side of a freight which is placed at a predetermined level.
The automatic transport vehicle described above is constructed to handle and transport the freight alone. Another known automatic transport vehicle is an automatic guided vehicle (AGV) that can automatically transfer a carriage either alone or together with a freight. The conventional AGVs are generally separated into a trailer type and a side-fork type depending on the system used therein for transporting the carriage.
In the trailer-type carriage transport system, the rear end of a vehicle body is coupled with the front end of a carriage or trailer via an automatic joint. Due to such joint structure, the behavior of the carriage being trailed is unstable, so the vehicle passage must be wide enough to provide a room for accommodating the irregular movement of the carriage. Furthermore, it is very difficult to transfer the carriage from the AGV to a transfer station. This difficulty is not the only technical problem to be solved but leads to a substantial increase in the cost of transportation.
The side-fork type carriage transport system requires a lift unit provided for hoisting a carriage and moving it with wheels of the carriage kept in a floating condition relative to the floor or the ground surface. The lift unit includes a lift mechanism which tends to increase the overall size of the lift unit due to the necessity of producing a desired power and providing a desired rigidity. Furthermore, the side-fork type requires a vehicle passage which is excessively larger in width than the vehicle width, in view of the occasions where the vehicle is to be turned to change the direction of movement to achieve a freight-transfer operation, and with a view to insure insertion and removal of the fork relative to the carriage. In addition, a sufficient vertical space must be provided to insure a lifting operation achieved when the carriage is transferred.
Among the conventional automatic transport vehicles described above, the AFT and the side-fork type AGV have a certain difficulty in reducing the overall size, require a vehicle passage which is excessively larger in width than the vehicle width, and further require a vertical space for ensuring the lifting operation. Thus, these automatic transport vehicles are defective in terms of cost and space.
On the other hand, the trailer-type AGV encounters a technical difficulty in transferring a carriage within a small space and should expect a substantial increase in the transportation cost.